1

A Coherent Approach for Interrogating 

Polybenzoxazole Fibers for Residual 

Phosphoric Acid

NISTIR 7584
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NISTIR 7584

A Coherent Approach for Interrogating 

Polybenzoxazole Fibers for Residual 

Phosphoric Acid 

Gale Holmes, Eun Su Park,

Charles Guttman and Kathleen Flynn 

Characterization and Measurement Group

Polymers Division

Materials Science and Engineering Laboratory

John Sieber

Inorganic Chemical Metrology Group

Analytical Chemistry Division

Chemical Science and Technology Laboratory

Stephanie Watson

Spectrochemical Methods Group

Materials and Construction Research Division

Building and Fire Research Laboratory

Kirk Rice

Office of Law Enforcement Standards

Electronics and Electrical Engineering Laboratory

December 2009

U.S. Department of Commerce

Gary Locke, Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Deputy Director
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Abstract

Because of the premature failure of in-service soft-body armor that contains the ballistic

fiber poly[(benzo–[1,2-d:5,4-d’]-benzoxazole-2,6-diyl)-1,4-phenylene] (PBO), the Office of Law 

Enforcement Standards (OLES) at the National Institute of Standards and Technology (NIST) 

initiated a research program to investigate the reasons for the failure and to develop testing 

methodologies and protocols to ensure that these types of failures do not reoccur. In a report that 

focused on the stability of the benzoxazole ring that is characteristic of PBO fibers, Holmes et al. 

(2006) showed that the benzoxazole ring was susceptible to hydrolytic degradation under acid 

conditions. Because of the processing conditions for the fibers, it is suspected by many 

researchers that residual phosphoric acid may cause the degradation of the benzoxazole ring that 

result in a reduction in ballistic performance. Prior to this work, no definitive data have

indicated the presence of phosphoric acid since the residual phosphorus is not easily extracted 

and the processed fibers are known to be laced with phosphorus containing processing aids. 

Methods to efficiently extract phosphorus from PBO are described in this report. Further, 

characterization determined that the majority of the extractable phosphorus in PBO was 

attributed to the octyldecyl phosphate processing aid with some phosphoric acid being detected. 

Analysis by matrix assisted laser desorption ionization of model PBO oligomers indicates that 

the non-extractable phosphorus is attached to the PBO polymer chain as a monoaryl phosphate 

ester. The response of model aryl phosphates to NaOH exposure indicates that the monoaryl 

phosphate ester is stable to the NaOH washes used in the manufacturing process to neutralize the 

phosphoric acid reaction medium and extract residual phosphorus impurities. These results 

strongly indicate that phosphoric acid that is chemically bound to the PBO molecule as a monoaryl phosphate ester is the primary cause for the hydrolytic degradation and that this residual acid 

type is not readily removed by caustic washes.

Acknowledgements 

The authors wish to thank the National Institute of Standards and Technology Office of Law

Enforcement and Standards (NIST-OLES) under the auspices of the National Institute of Justice 

(NIJ) for funding this work under interagency agreement 2003-IJ-R-029. NIJ is not responsible 

for the content of this article.
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1 INTRODUCTION

The poly[(benzo–[1,2-d:5,4-d’]-benzoxazole-2,6-diyl)-1,4-phenylene] (PBO) fiber is part 

of a sub-class of rigid-rod polymers known as polybenzazoles (PBXs). PBO evolved out of the 

pioneering research of Vogel and Marvel [1,2] on thermally stable polybenzimidazole (PBI), a 

related PBX polymer. Although PBO can be found in a variety of applications, the primary use 

for this polymer has been in the manufacture of soft body armor (SBA) for civilian first 

responder applications, where its superior properties relative to polyaramids (i.e., Kevlar, 

Twaron) [3] ushered in the development of ultra-lightweight SBA.

PBO is prepared by the reaction of 1,3-diamino-4,6-dihydroxybenzene (DADHB) 

dihydrochloride with terephthalic acid (TA) in a reaction medium consisting of polyphosphoric 

acid (PPA) enriched with P2O5 as a dehydrating agent. Although the fibers have superior tensile 

strength and modulus, cut and abrasion resistance, and flame retardation relative to other high 

performance fibers, concerns have recently been expressed recently about the long-term stability 

of PBO fibers [4]. Several studies indicate a reduction in the mechanical properties of PBO (i.e., 

strain-to-failure, ultimate tensile strength) when exposed to moisture [3,5]. To better understand 

these concerns, the reaction scheme adapted from the research of So et al. [6,7] is shown in 

Figure 1, where the key feature in the PBO reaction is the formation of the benzoxazole ring 

structure. The influences of pH, ultraviolet (UV) radiation, and other factors on the stability of 

this ring have recently been reviewed by Holmes et al. [8], with literature results indicating that 

the acid-catalyzed pathway to hydrolysis of the benzoxazole ring in PBO is feasible, but pH 

sensitive. 

In the reaction scheme shown in Figure 1, the carbonyl group in TA initially reacts with 

PPA to form a carboxylic-phosphoric mixed anhydride (Species A). The hydroxyl groups of 

protonated DADHB, which are also in equilibrium with PPA as DADHB-PPA (aryl-phosphate) 

esters, reacts with the mixed anhydride to form esters (Species B). Species B then undergoes the 

expected Railford acyl migration [8] to form an amide prior to the ring closure reaction that 

forms the benzoxazole ring (Species C). Reaction of Species C, 2,2’-(1,4-phenylene)bis(5-

amino-6-benzoxazolol), with Species A leads to the formation of the PBO polymer where the 

PBO oligomers are preferentially capped with DADHB. The terminal DADHB groups have un-
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reacted hydroxyl groups in the reaction medium that are in dynamic equilibrium (i.e., partially 

reacted) with PPA to form aryl-phosphate esters.

Elemental analysis indicates that processed PBO fibers have a residual phosphorus (P) 

mass fraction of approximately 0.3 % to 0.4 % [3,4,9,10]. This observation and the synthesis of 

PBO in PPA have led many researchers to make the plausible assumption that the residual 

phosphorus in PBO fibers is due to phosphoric acid (PA) and to infer that PA catalyzes the 

mechanical property degradation observed in PBO fibers. This assumption is based on the 

research of Jackson et al. [11] who showed that under acidic conditions simple benzoxazoles 

hydrolyze principally to the corresponding amidophenols. Two research reports [4,5] provide 

indirect evidence of the PA catalyzed hydrolysis reaction. In refererence 5, the tensile strengths 

of PBO fibers are found to decrease when phosphorus mass fraction is increased above 1 % by 

exposing the fibers to increasing amounts of phosphoric acid. In the manufacture of PBO fibers, 

a residual phosphorus level between (2000 to 5000 mg/kg) is generally targeted [12]. This is 

particularly important when one observes that the severe conditions achieved by exposing PBO 

fibers to phosphoric acid are unlikely to be encountered in normal applications. 

Furthermore, it is noted that extreme washing treatments (boiling water or Soxhlet 

extraction) are not effective in lowering the phosphorous content in as-spun dried or heat treated 

fiber samples. Research by others [9] indicates that the residual phosphorus mass fraction in 

PBO fibers can be reduced from 0.4 % mass fraction to just 0.25 % mass fraction by washing the 

fibers with supercritical carbon dioxide. Finally, a recent investigation performed at the National 

Institute of Standards and Technology (NIST) exposed soft body armors composed of PBO 

fibers to a constant hydrolytic environment for six months. Consistent with previous research, 

chemical degradation of the fibers was observed by difference Fourier transform infrared (FTIR) 

spectroscopy [10]. 

All extant research [3-5,10,13] indicates that PBO fibers are degraded by hydrolytic 

action, which researchers presume to be catalyzed by residual PA. Complicating this seemingly 

straight forward interpretation is the absence of direct evidence for the existence of PA in 

processed PBO fibers and the knowledge that alkyl-phosphate esters are often used as processing 

aids during the manufacture of PBO fibers. Therefore, the research in this report will focus on 

the development of a direct approach for identifying phosphoric acid in the presence of alkyl-
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phosphate esters that may be present and to provide additional insight as to the nature of the 

seemingly non-extractable phosphorus found in PBO fibers. 

In this report, X-ray fluorescence (XRF) spectrometry along with standard derivatization 

procedures, extraction techniques, and model compounds are used to develop a coherent 

approach for interrogating PBO fibers for the presence of residual phosphoric acid compounds. 

Because of the insolubility of PBO oligomers and pre-polymeric species in most solvents, matrix 

assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is also 

employed to identify species in polymer oligomers. A dual injector gas chromatograph/mass 

spectrometer (GC/MS) is used in electron impact (EI) and chemical ionization (CI) modes to 

obtain fragmentation spectra and molecular ion data for extracted low molecular mass species. 

To unequivocally identify phosphorus extracted compounds, a parallel flame photometric

detector (FPD) and a non-parallel nitrogen phosphorus detector (NPD) are also used.

2 EXPERIMENTAL

Materials: 2,2’-(1,4-phenylene) bis(benzoxazolyl) (AF1), 2,6-diphenylbenzo[1,2-d;5,4-

d’]bisoxazole (AF2), and 2-phenylbenzoxazole (AF3), model compounds of PBO, were supplied 

by the Wright Patterson Air Force Research Laboratories (see Figure 2), with the relationship of 

these model compounds to the PBO chain structure shown in Figure 3. PBO fibers were 

obtained from a field returned vest supplied by the Department of Justice. Phosphoric acid, 

phosphorous pentoxide, 2-phenylbenzoxazole (PBOm), 4,6-diaminoresorcinol (DADHB), 2-

aminophenol (2-AP), terephthalic acid (TA), trimethyl phosphate (TMP), triphenyl phosphate 

(TPhP), sodium phenyl phosphate dibasic dihydrate (DNaPhP), sodium hydroxide and 

concentrated hydrochloric acid (HCl, 37 % mass fraction) were purchased from Aldrich 

Chemical Co.1 and used as received. HCl used in this study has phosphorus (P) < 0.01 mg/kg

(Fluka data). 

 1Certain commercial products and equipment were named in this paper for the purpose of adequately specifying the 

experimental conditions and the sources of analytical results. Such descriptions do not constitute endorsement by 

the National Institute of Standards and Technology, nor do they imply that the equipment and products are 

necessarily the best for the purpose.
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Synthesis of PBO oligomer: The synthesis method was adapted from references 14 and 15. In 

this study, 2-AP was added as an end-capping material to keep the molecular mass of the PBO 

oligomer in a range that could be analyzed by MALDI-TOF MS. Poly(phosphoric acid) was 

prepared by the following method. Phosphorous pentoxide (500 g) was added slowly to 196 mL 

of 85 % PA while the mixture was stirred under nitrogen. The mixture was then heated at 150 oC 

for 12 h to yield a homogeneous (clear) solution of PPA. 

After the temperature of PPA was decreased to 80 oC, 5.00 g (0.0235 mol) of 

4,6-diaminoresorcinol and 0.51 g (0.0047 mol) of 2-AP were added under a slow stream of 

nitrogen, and the mixture was heated at 80 oC for 16 h. Then the mixture was heated at 110 oC 

for 8 h until the evolution of HCl ceased. Terephthalic acid (TA) in the amount of 4.29 g 

(0.0258 mol) was added, and the mixture was heated at 150 oC for 12 h followed by 175 oC for 

4 h. The brown solution was poured into water and washed with distilled water and dried. The 

oligomer was then washed 10 times with 1 L aliquots of 52 oC water, dried, and rewashed 10 

additional times with 1 L aliquots of 75 oC water. 

1st Soxhlet extraction of 1st PBO fibers: A total of 10 g of PBO fibers (1st Fiber as received) 

were placed in a thimble made from filter glass, which is loaded into the main chamber of the 

Soxhlet extractor. About 1 L of distilled water was used as the extraction solvent and was 

refluxed for 7 d. This was done to remove all loosely bound phosphorus-containing species and 

additives. The fibers were tested using XRF before and after the extraction procedure to 

determine the amount of removed phosphorus. The extraction fluid was placed in an oven at 52 

oC and reduced in volume to about 10 mL. This fluid (1st Water Extract of 1st Fiber) and a blank 

of water run through the same Soxhlet extraction and evaporation procedure were analyzed by 

XRF and GC/MS. 

1st Soxhlet extraction of 2nd and 3rd PBO fibers: The same procedure described above was 

repeated with the 2nd and 3rd sets of PBO fibers, which were from different manufacturing lots. 

Samples derived from the Soxhlet procedure are labeled as follows: 2nd Fiber as received, 1st

Water Extract of 2nd Fiber, 1st Extract Fiber of 2nd Fiber, 3rd Fiber as received, 1st Water Extract 

of 3rd Fiber, and 1st Extract Fiber of 3rd Fiber.
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Soxhlet extraction of PBO oligomers: Synthesized PBO oligomers were also extracted by the 

Soxhlet procedure described above for 14 d and analyzed by XRF, MALDI-TOF MS, and 

GC/MS.

2nd Soxhlet extraction of 1st PBO fibers: A 7.8 g quantity of the extracted PBO fibers (1st

Extract Fiber of 1st Fiber) was placed between sheets of weighing papers (VWR Scientific 

Products) and then crushed with a mortar and pestle chilled using liquid nitrogen to help expose 

the microscopic voids found in PBO fibers (see Figure 4) to the water extractant. These crushed 

fibers were then extracted for 14 d with 800 mL of distilled water by the Soxhlet procedure 

described above. Phosphorus content in the fibers was monitored by XRF analyses before and 

after the 2nd Soxhlet extraction. The final extracted fiber was labeled as (2nd Extract Fiber of 1st

Fiber). The extractant was concentrated to 15 mL. Fibers (2nd Extract Fiber of 1st Fiber) and the 

extractant (2nd Water Extract of 1st Fiber) were analyzed by MALDI-TOF MS and GC/MS to 

identify the species removed from the PBO fibers.

1st Caustic treatment on 2nd Extract Fiber of 1st Fiber: A 3.54 g portion of 2nd Extract Fiber

of 1st Fiber was refluxed in 1 L of 0.1 mol/L NaOH solution for 7 d. After cooling down, the 

fibers (1st Caustic treated Fiber of 1st Fiber) were separated from the solution and dried in air. 

The solution (1st Caustic solution of 1st Fiber) was concentrated in the 52 oC oven to 10 mL. 

XRF measurements were done before and after the 1st Caustic treatment.

2nd Caustic treatment on 1st Caustic treated Fiber of 1st Fiber: A 3 g quantity of 1st Caustic 

treated Fiber of 1st Fiber was refluxed in 1 L of 1 mol/L NaOH for 7 d. Fibers (2nd Caustic 

treated Fiber of 1st Fiber) were separated and dried in air. The solution was concentrated in air 

to about 100 mL then acidified with concentrated HCl to approximately pH 4. NaCl and SiO2

precipitated during acidification and were removed by filtration. The acidified solution was 

concentrated to 10 mL. Salts precipitated during concentration were removed by filtration. 

Fibers before and after this caustic treatment were analyzed by XRF. The concentrated solution 

(2nd Caustic extract solution of 1st Fiber) was analyzed by GC/MS after methylation.
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1st Caustic treatment on 2nd PBO fibers: The same caustic extraction procedure was applied 

to 1st Extract Fiber of 2nd PBO fibers. Samples were labeled 1st Caustic extract solution of 2nd

Fiber and 1st Caustic treated Fiber of 2nd Fiber.

Test of Stability of Chemically Bound Non-Extractable Phosphorus: One of the two theories 

that have been advanced to explain the non-extractable phosphorus in PBO fibers suggests that 

the phosphorus is chemically bound to the polymer as aryl-phosphate esters. These arylphosphate esters in the final product are thought to arise from the known equilibrium reaction of 

PPA with the un-reacted hydroxyl groups of DADHB (Figure 1), with the NaOH neutralization 

and washing procedure not affecting their complete removal. Interestingly, literature results 

indicate that phenyl phosphates can be hydrolyzed under the caustic conditions that are normally 

used to wash the process fibers. Triphenyl phosphate (TPhP) and sodium phenyl phosphate 

dibasic dihydrate (DNaPhP) were used as model compounds to test the stability of arylphosphate esters exposed to caustic materials. 

A mass of 11.3 mg of TPhP was added to 28 mL of 1 mol/L NaOH solution in a single 

neck, 100 mL round-bottom flask equipped with a condenser. The mixture was refluxed for 7 d. 

This mass of TPhP corresponds to 1.1 mg phosphorus. According to XRF results, 8.9 mg of P is 

present in 3.54 g of PBO fiber after two aqueous Soxhlet extractions and treatment of these 

fibers with a 0.1 mol/L NaOH solution. Under the test conditions, TPhP melted during boiling, 

but remained immiscible with water. After cooling, the contents of the flask were acidified by 

adding concentrated HCl. Precipitated solids (remaining un-reacted TPhP, NaCl and SiO2) were 

removed by filtration, and the remaining solution was concentrated to 10 mL. Salt generated 

during the concentration was also removed by filtration and then extracted with diethyl ether for 

analysis by GC/MS. The concentrated diethyl ether extract and the concentrated solution were 

modified by the methylation procedure for further analysis.

The same caustic treatment procedure was performed on 7.56 mg of sodium phenyl 

phosphate dibasic dihydrate (DNaPhP) in 28 mL of 1 mol/L NaOH. DNaPhP was soluble in 

caustic water. The solution was acidified and concentrated to 10 mL after boiling for 7 d. Solids

precipitated during the procedure were removed by filtration. An aliquot of 0.5 mL of the 

concentrated solution was modified by methylation for GC/MS analysis. This procedure was 
10

repeated on 10.4 mg of sodium phenyl phosphate dibasic dihydrate in 38 mL of 1 mol/L 

methanol NaOCH3 solution.

UV-Irradiation: Ultraviolet (UV)-irradiation was performed with an apparatus equipped with a 

1000 W xenon arc lamp (Oriel Corp). The device used in these experiments is shown in Figure 

5, with the spectral output of the unit with the various attachments shown in Figure 6. Because 

of the exposure hazards associated with UV radiation, the device was operated according to the 

safety precautions in the standard operating procedure located in Appendix A. 

A 4.98 g quantity of 1st Caustic treated Fiber of 2nd Fiber was dipped into 200 mL of 

acidified water (pH 4) and divided into three portions. Each sample was placed in a wide-mouth 

beaker which was placed horizontally in the Oriel apparatus. Light intensity at the sample site 

was measured with a Newport Radiant power meter and probe, models 70260 and 70268, 

respectively. The light intensity at the sample was about 950 W/m2

. Each portion was exposed 

to UV radiation with no filters for 25 h, during which the acidified water was replenished by 

adding 50 mL every 8 h to prevent the sample from going to dryness (open container approach). 

After the UV irradiation, the fibers were gathered from the beaker, squeezed to remove liquid,

and dried in air. The liquid was concentrated to 21 g, and then 1.7 g was methylated to facilitate 

GC/MS measurement. 

A second procedure was performed in a sealed “quartz” chamber. The quartz container 

was made from a 15.56 cm (6 1/8 in) x 15.56 cm (6 1/8 in) x 5.08 cm (2 in) rectangular PMMA 

[i.e, poly(methyl methacrylate)] container with the two-piece top and bottom PMMA plates 

containing 10.16 cm (4 in) x 10.16 cm (4 in) quartz windows. The top and bottom acrylate

plates were fixed to the rectangular acrylate box by removable screw bolts. In the top PMMA 

plate, two Teflon [i.e., poly(tetrafluoroethylene)] screw stoppers were included to facilitate the 

injection and extraction of liquid (see Figure 7, sealed container approach). A quantity of 3 g of 

2nd Caustic treated 1st Fiber, 400 mL of acidified water (pH 4), and a magnetic stirring bar were 

put into sealed quartz chamber. The chamber was subsequently exposed to unfiltered UV 

radiation for 7 d while stirring. The fibers were removed from the chamber and filtered with a 

Buchner funnel utilizing Whatman filter paper. The filtrate was concentrated to 10 mL, 

methylated and then analyzed by GC/MS. The amount of phosphorus in fibers before and after 

UV-treatment was analyzed by XRF.
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The sodium phenyl phosphate dibasic dihydrate (DNaPhP) compound was also subjected 

to UV irradiation. A quantity of 12.7 mg of DNaPhP was put into 12.5 g of acidified water 

(pH 4) in a quartz container, which was then sealed with a Teflon stopper (sealed container 

approach). The contents were exposed to UV radiation with no filters. Aliquots of 0.5 mL were 

taken from the container after 0 h, 2 h, 12 h and 24 h for methylation and GC/MS analysis. 

Methylation methods: The Soxhlet extracts were methylated using an in situ consumption 

diazomethane generator (see Figure 8). The generator is composed of three test tubes arranged 

in a stair-step fashion with test tube 1 being the highest in the arrangement. Since diazomethane 

presents an explosion hazard, the safety precautions listed in the standard operating procedure 

found in Appendix B were used. Although this approach is typically used for the methylation of 

carboxylic acids, diazomethane is also known to react with other compounds that have labile 

hydrogens such as phosphoric acid (see Figure 9) [16].

A quantity (10 mL) of peroxide-free diethyl ether was added to test tube 1, and the 

nitrogen pressure was adjusted to give a smooth bubbling in test tube 1. A mixture of about 

4 mL of a 37 % mass fraction KOH solution in distilled water and 6 mL of carbitol was added to 

test tube 2 and again the nitrogen pressure was adjusted to give a smooth bubbling in test tubes 1 

and 2.

Approximately 1 mL of each concentrated aqueous extract along with 5 mL of diethyl 

ether:ethanol (3:1) mixture was added to test tube 3. The diethyl ether:ethanol mixture was used 

rather than diethyl ether alone to provide a homogeneous mixture with the aqueous solution. 

Earlier research [17] supports this approach since diazomethane reacts with water to form 

methanol. Again the nitrogen pressure was adjusted to yield uniform bubbling in all three test 

tubes. Approximately 1.0 g to 1.5 g of diazald was added to test tube 2. After 6 min, additional 

diazald was added to test tube 2, and the reaction was continued until the sample in test tube 3 

turned yellow, indicating the complete reaction of labile protons. Nitrogen was then blown over 

the sample in test tube 3 to evaporate residual solvents.

The solid flakes that were detected on the PBO fibers after boiling them in NaOH were 

also methylated after the following sample preparation. The solids were dissolved in an 80:20 

mixture of 3:1 ether:ethanol mixture with H2O. This combined mixture of ether, ethanol and 

water was acidified with concentrated HCl and methylated as described above. 
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Measurements: 

LDI- and MALDI-TOF MS 

Mass spectra were obtained using a Bruker Daltonics (Billerica, MA) REFLEX II 

spectrometer. The acceleration voltage was 25 kV and the reflectron mode was used. Delayed 

extraction was 0.750 μs. A nitrogen laser at 337 nm was employed as a source. External mass 

calibration was performed using CsI2. The resolution of the instrument is 20,000 atomic mass 

units (amu).

Samples were prepared by the following methods. For solid samples such as AF1, AF2, 

AF3, PBOm and PBO oligomer, a small quantity of sample was ground with 20 μL of THF/HCl 

mixture (2 mL/1 drop) using a mortar and pestle until most of the solvent evaporated. The sticky 

sample for doing LDI-TOF-MS was pressed using a spatula onto the stainless steel substrate 

which was covered by Parafilm. For liquid samples such as extracts, 1 mL was concentrated in 

an oven at 52 oC. Samples were prepared using a variety of matrix/salt conditions: THF/HCl 

mixture (2 mL/1 drop), acetonitrile/0.1 % of TFA solution (1:1 by volume), and sinapinic acid in 

THF (10 mg/mL)/Na TFA in THF (10 mg/mL) (1:1 by volume). The prepared samples were 

spotted onto a stainless steel plate and air-dried (see Figure 10). From these sample preparations, 

a methodology was developed for identifying intractable PBO oligomers by testing the AF1, 

AF2, and AF3 model compounds using MALDI-TOF MS (see Figure 11 and Figure 12).

GC/MS

The GC/MS procedure for analyzing the methylated products was developed by 

subjecting phosphoric acid to the above methylation procedure and detecting the trimethyl ester 

of phosphoric acid and the associated impurities that may arise from the methylation procedures. 

A representative example of the total ion current trace showing the trimethyl ester of phosphoric 

acid and stuctures of the compounds associated with the methylation procedure are shown in 

Figure 13 with the identification of the associated compounds given in Figure 14. 

All methylated aqueous solutions were concentrated to approximately 0.5 mL. The 

methylated products were then extracted into about 3 mL of diethyl ether. The diethyl ether 

solution was then concentrated to approximately 1 mL. These concentrated samples were then 
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analyzed by GC/MS with the specific equipment being a dual injector Trace GC 2000 gas 

chromatograph interfaced to a Trace DSQ II mass spectrometer (MS, Thermo Finnegan – see 

Figure 15). The resolution of the instrument is 1,200 amu. The GC was also equipped with a 

flame photometric detector (FPD) and a nitrogen/phosphorus detector (NPD). The GC is 

equipped with a split/splitless (S/SL) injector and a programmable temperature vaporizing (PTV) 

injector. The effluent from a 15 m x 0.25 mm ID x 0.25 μm Rxi-5MS capillary column attached 

to the PTV injector was split to the FPD and MS using a MS-column flow splitter (SGE 

Analytical Science). This device equalizes the retention times between the FPD and MS 

detectors, thereby allowing for phosphorus containing compounds to be distinguished in the 

GC/MS chromatogram. A second 15 m x 0.25 mm ID x 0.25 μm Rxi-5MS capillary column

attached to the second injector (S/SL) and connected directly to the NPD detector provides 

additional information about phosphorus containing compounds. Sample volumes of 1 μL were 

injected with splitless mode. Helium was the carrier gas (flow rate: 1 mL/min). The oven was 

programmed with an initial temperature of 50 oC and a hold time of 1 min. The GC oven

temperature was raised 20 oC/min up to 260 oC and held at 260 oC for 10 min. The DSQ II mass 

spectrometer acquired electron impact (EI), and/or chemical ionization (CI), full scan data, with 

a mass range of 50 u to 600 u, where 1 u = 1 g/mol. The x-axis of the mass spectra shown in 

Figure 17 and Figure 18 are give in terms of m/z (mass-to-charge) ratio. This unit is not an SI 

unit since the lowercase m is the SI unit for meter. The correct unit for mass is u, the unified 

atomic mass unit. A more correct unit for use on the x-axis for each mass spectrum would 

therefore be u/z. However, mass spectrometrists simply choose not to use it [18]. 

XRF

Fiber samples, liquids, and key ingredients in the synthesis and extraction experiments 

were analyzed by XRF for the purpose of detecting elements present and determining the 

approximate mass fractions of those elements other than H, C, O, and N. The materials used in 

the work described in this paper consisted of bunches of fibers, liquids from extraction or 

derivatization experiments, and various solid products from the experiments such as flakes of 

dried material or partially ground fibers. High-performance elemental analyses, viz. quantitative 

analyses, of such a variety of materials would normally be expensive and time consuming 

whether done by XRF or another available test method. Because the experiments in this paper 
14

were viewed as investigative in nature, it was decided to emphasize speed and comparability 

over quantitative results. This is justified because every sample required a qualitative analysis to 

identify elements present and a “semiquantitative” analysis to find approximately how much of 

each element was present. The experiments that produced the samples were expected to effect 

substantial changes in compositions or no changes at all.

Fundamental Parameters (FP) XRF methods are well suited to this investigative realm. 

FP XRF methods are designed to be interactive and are implemented as sophisticated computer 

programs. The investigator can specify to the computer program all a priori knowledge of the 

chemical and physical properties of each specimen. As an example, the PBO fibers were 

specified as having a chemical formula of C14H10N2O2, which was chosen as the balance 

compound because FP XRF methods solve a set of equations with the SUM = 100 % constraint. 

Similarly, aqueous solutions were specified with H2O as the balance compound, and white flakes 

found in some fibers were specified with C6H10O5 (a general formula for cellulose from filter 

paper) as the balance compound. In some cases, the elements of interest were specified as 

oxides, when there was evidence that additional oxygen was present beyond the PBO 

compounds. However, in nearly all cases, the inorganic elements in the fibers were simply 

calculated as the elements. 

The FP XRF program used in this work was the IQ+ method from PANalytical, Inc 

(Almelo, The Netherlands), which was run in the SuperQ operating system, version 4.0d, of a 

model PW2404 wavelength-dispersive spectrometer, also from PANalytical, Inc. The IQ+ 

method was calibrated using a set of glass and briquette standards provided by the vendor, which 

was bolstered by a number of NIST Standard Reference Materials. This calibration scales the 

calculations to the actual performance of the spectrometer employed in this effort. The program 

was originally calibrated in 2001 and has been maintained by implementing drift correction 

updates since that time. All measurements were made in scanning mode, in vacuum for solids or 

He for liquids, with the Rh anode X-ray tube operated at 3 kW. As was mentioned, physical 

properties of the specimens may be included to help set boundary conditions for the FP 

calculations. All specimens were weighed into sample cells, and an estimate of the viewed area 

was made. These values were entered into the program to help scale the expected X-ray count 

rates calculated from the FP equations. The cells were 25 mm polyethylene (Somar, Las Vegas, 

NV) with 6 mm polypropylene window material.
15

The performance of FP XRF methods such as IQ+ can best be described as 

“semiquantitative” in that it varies from quantitative with well-controlled specimens to ‘order of 

magnitude’ results, when specimens are difficult to handle, of very small quantity, or have some 

other complicating properties. The PBO fiber specimens are of moderate difficulty to analyze 

because they are a challenge to present to the spectrometer for measurements. XRF methods are 

at their best when all specimens are of the same physical characteristics in that they have the 

same size, shape, and mass, and when all of their constituent elements can be measured and 

directly calculated as mass fractions summing to 100 %. PBO fibers, powders, water solutions, 

and the like do not conform to this ideal situation. The fibers cannot be positioned inside cells in 

a perfectly repeatable manner because they do not lay flat on the inside bottom of the cell. Water 

and organic materials are mostly C, N, and O, which cannot be measured when the specimen is 

placed inside a cup-shaped cell. The fluorescent X rays from these elements cannot penetrate the 

thin polymer window supporting the specimen at the bottom of the cell. 

The uncertainty of XRF results was evaluated by analyzing specimens of SRM 1575a 

Pine Needles, which contains 0.107 % total P. Measured results for P in SRM 1575a ranged 

from quantitative when sufficient sample mass was provided to biased low by approximately 

35 % when the sample mass was only 20 mg. The results for other elements present in SRM 

1575a were observed to be biased either high or low by amounts ranging from 50 % to a factor 

of 10 depending on the mass of sample, the element, and the energy of the X-ray line measured 

for that element. On the Certificate of Analysis, it is recommended to use at least 250 mg of 

SRM 1575a for a determination. In addition, quantities < 100 mg did not cover the entire viewed 

area of the specimen cup, and results were low because P K-L2,3 X rays are of low energy and do 

not penetrate deeply into most materials. Therefore, samples of low mass and uneven 

distribution in a cell are expected to yield biased results. This source of bias is expected to affect 

the PBO and other samples studied in this work. The results for P reported in Table 1 have been 

assessed an overall relative uncertainty based on a non-symmetrical, triangular distribution of 

+ 10 % to - 50 % relative (approximate 95 % level of confidence) based on the observed 

performance for SRM 1575a. However, comparisons of values in Table 1 should be viewed in 

the context of the expected repeatability of measurements for the IQ+ method. Based on past 

performance of the method, the relative standard deviation for repeatability is approximately 
16

10 %. The additional elements reported in Table 1 are provided for forensic purposes. For each 

element, differences of a factor of two or greater may be significant.

3 RESULTS AND DISCUSSIONS

Based on the nomenclature in prior accounts [4,9,10], the results will be discussed in 

terms of extractable and non-extractable phosphorus in PBO fibers. Extractable phosphorus is 

defined as the phosphorus removed during the water Soxhlet extraction procedure, while nonextractable phosphorus is defined as requiring mechanical or chemical means to remove it from 

the fiber.

3.1 Extractable Phosphorus in PBO Fibers

With recognition of the possible presence of phosphorus-containing processing additives 

in manufactured PBO fibers, the Soxhlet extraction method was employed to separate free acid 

species from non-extractable phosphorus. Table 1 shows XRF results for the PBO fibers before 

and after Soxhlet extraction and the extracted solutions. Consistent with previous research, the 

1st set of PBO fibers were found to contain about 0.38 % phosphorous by mass. After Soxhlet 

extraction for 7 d, data from the 1st set of PBO fibers indicates that 75 % of the phosphorous 

remained in the fibers. The phosphorus level in the 1st set of PBO fibers is consistent with PBO 

fiber analyses from previous research [9,10]. Additionally, the amount removed by Soxhlet 

extraction is consistent with the quantity removed by super critical fluid extraction [9]. 

Comparatively, the initial phosphorus levels in the 2nd and 3rd sets of PBO fibers were 16 % and 

37 % lower, respectively, than the 1st set of PBO fibers. These reductions may reflect 

inconsistencies in the NaOH washing procedure during manufacturing or a change by the 

manufacturer to a more efficient washing process. Consistent with the 1st set of PBO fibers, the 

Soxhlet extraction procedure removed little or none of the residual phosphorus from the as 

received samples. Furthermore, a subsequent Soxhlet extraction of the 1st set of PBO fibers after 

they were damaged by crushing caused no additional reduction in the level of phosphorus, 

further suggesting that the remaining phosphorus is not extractable. 

In the 1st set of PBO fibers, the aqueous extract was concentrated and acidified with HCl 

to convert any extracted acid salts to the free acid. An attempt was made to extract these 
17

phosphorus species into diethyl ether for the methylation procedure with no success. For the 2nd

and 3rd PBO fiber samples, the extracted phosphorus containing species were also concentrated 

as describe in the Experimental Section and acidified with HCl. In a departure from the 

procedure used on the extractant from the 1st set of PBO fibers, a 1 mL portion of the 

concentrated extract was mixed with a 3:1 diethyl ether:ethanol mixture, methylated as described 

in the experimental section, and analyzed by GC/MS under electron impact (EI) and chemical 

ionization (CI) test conditions along with FPD and NPD detection. 

The total ion current (TIC) chromatograms and the parallel FPD chromatograms are 

shown in Figure 16 for the samples run under EI and CI test conditions. In the FPD 

chromatograms (Figure 16(b) and Figure 16(d)), two peaks at retention times of 4.12 min and 

14.16 min under EI conditions and 3.77 min and 13.42 min under CI conditions are shown that 

indicate phosphorus containing compounds. The EI and CI mass spectra of the first peak are 

shown in Figure 17(a) and Figure 17(b). From Figure 17(b), the characteristic ions parent+1 u, 

parent+29 u, and parent+41 u observed under CI conditions indicate that the molecular mass of 

the first eluting phosphorus containing species is 140 u. The EI spectrum, which is consistent 

with the published spectrum of the trimethyl ester of phosphoric acid (CAS # 512-56-1) [19,20], 

indicates the successive loss of two units of 30 u from the parent ion (140 u) and the parent-1 u 

ion to form the fragment ions observed at 110 u and 80 u and 109 u and 79 u, respectively. The 

losses from the parent ion have been shown to be exclusively linked to the elimination of the 

neutral species CH2O [20]. Therefore, the EI and CI spectra of the first eluting peak indicate the 

presence of extractable phosphoric acid from the PBO fibers.

From Figure 17(d), ions at 379 u, 407 u, and 419 u in the second eluted peak correspond 

to the characteristic ions mentioned above for CI molecular ion determination and indicate that 

the molecular mass of this species is 378 u. The absence of the corresponding molecular ion 

under EI conditions (Figure 17(c)) and the indication from Figure 16(b) and Figure 16(d) that 

this compound contains phosphorus suggest that this species may be a phosphate ester with a 

long alkyl chain. The dominant fragment ion at 127 u can be assigned to the structure shown in 

Figure 17(c), further supporting the identification of this species as a long alkyl chain, 

dimethylester phosphate, where the dimethyl ester groups on this trialkyl phosphate ester arise 

from the methylation procedure. 
18

It is known that ethyl and higher alkyl phosphate esters undergo the classic 

McLafferty + 1 rearrangement to eliminate the alkyl groups as a radical from the molecular ion 

[21]. Furthermore, the EI mass spectrum of the diethyl pentyl ester of phosphoric acid 

(DEPEPA, relative molecular mass = 224 u, CAS # 20195-08-8) contains the corresponding 

rearrangement fragment ion at 155 u, which reflects the presence of the diethyl groups rather 

than the dimethyl groups indicated on the 127 u fragment ion found in Figure 17(c). Successive 

losses of 28 u below the 155 u fragment ion are observed in DEPEPA that probably correspond 

to successive losses of the neutral species C2H4. These losses are not observed in Figure 17(c). 

Finally, the published spectra of the trimethyl silyl (TMS) derivative of 1-dodecyl-d25 phosphate 

also exhibits the characteristic McLafferty + 1 rearrangement to eliminate the deuterated dodecyl 

alkyl group as a radical from the molecular ion (see Figure 18) [22]. From these observations, 

the second phosphate compound seems to be an octadecyl dimethyl ester of phosphoric acid. 

This identification indicates that octadecyl phosphate or the disodium salt of octadecyl phosphate 

is being used as a processing aid by the manufacturer.

It is worth noting that even though the semi-quantitative XRF analyses of the 2nd and 3rd

sets of PBO fibers before and after Soxhlet extraction showed little or no discernible differences 

in phosphorus levels, the extractant from the 2nd set of PBO fibers showed by GC/MS, one of the 

most sensitive analytical tools for detecting unknown compounds, the presence of extractable 

phosphoric acid and n-octadecyl phosphate. This indicates that in these latter sets of PBO fibers, 

the majority of the residual phosphorus is non-extractable.

3.2 Non-Extractable Phosphorus in PBO Fibers

Two theories have been put forth to explain the presence and nature of the nonextractable phosphorus. The first theory suggests that phosphoric acid may be trapped in 

microscopic voids that are known to exist along the length of the PBO fiber (see Figure 4). In 

the presence of moisture, the trapped phosphoric acid in these microscopic voids is suspected of 

lowering the localized pH in the PBO material surrounding them, thereby creating a localized 

environment conducive to hydrolytic degradation. The second theory suggests that the residual 

phosphoric acid, if present, may be chemically bound to the PBO polymer chain structure as a 

monoaryl phosphate ester (see Figure 19).
19

To address the first theory a second extraction was performed on the 1st set of PBO fibers 

that had been previously extracted with water by the Soxhlet procedure. These fibers were cut 

into small pieces and ground with a mortar and pestle cooled by liquid nitrogen in an attempt to 

disrupt the microscopic voids and make them more accessible to moisture. Although a semiquantitative assessment of the damage caused by grinding the fibers was not obtained, XRF 

results for the cut and ground fibers did not show a decrease of the amount of phosphorous

compared to the analysis after the first extraction (see Table 1). Consistent with these results, 

XRF results for the 2nd extracted solution from the 1st set of PBO fibers indicated the presence of 

phosphorous comparable to that of the water blank. This result suggests that either the fibers 

were not sufficiently damaged by the crushing procedure or phosphoric acid is not trapped in the 

microvoids.

To pursue the second theory, the twice extracted fibers from the 1st set of PBO fibers 

were boiled for 7 d in 0.1 mol/L NaOH caustic solution. A small decrease in the phosphorus 

level was observed by XRF. The boiling experiment was repeated with 1 mol/L NaOH, with no 

observable change in phosphorus levels. To verify these results, the 2nd set of PBO fibers was 

boiled with 1 mol/L NaOH. Consistent with the 1st set of PBO fibers the phosphorus level 

decreased slightly from 0.29 % mass fraction to 0.27 % mass fraction (see Table 1). A recheck 

of the 1st set of PBO fibers after boiling in NaOH revealed the presence of solid flakes in these 

fibers. Reanalysis of the twice Soxhlet extracted and twice NaOH boiled 1st set of fibers after 

removal of the flakes showed them to exhibit no change or a slight increase in the phosphorus 

level. The amount is also comparable to that found in the 2nd set of PBO fibers after Soxhlet 

extraction and treatment with 1 mol/L NaOH. 

The solid flakes were found to contain sodium, silicon, with some phosphorus. After 

acidifying the solids and methylating the resulting aqueous solution, octadecyl phosphate, with 

no indication of phosphoric acid, was detected. The presence of this processing additive after 

boiling in the NaOH, may reflect the increased solubility of disodium octadecyl phosphate in 

water relative to octadecyl phosphate. It should be noted that the basic solutions from these 

NAOH treatments did not indicate the presence of phosphorus by XRF and after they were 

concentrated, acidified, and methylated for analysis by GC/MS. Therefore, the NaOH treatments 

appear to slightly lower the level of phosphorus in the fibers that have been previously subjected 
20

to the Soxhlet extraction procedure by converting the remaining octadecyl phosphate, which has 

limited solubility in water, to the more water soluble disodium salt. 

In a parallel investigation, the phosphorus level in low-mass average molecular mass 

model PBO oligomers were investigated with the goal being to look for the presence of 

phosphorus containing species in these intractable model oligomers by MALDI-TOF MS. After 

extensive rinsing of the model PBO oligomers with water, the final phosphorus level by XRF 

was 1.4 % (see Table 1). Soxhlet extraction of these oligomers reduced the phosphorus level to 

0.062 % mass fraction, with GC/MS identifying the phosphorus species in the aqueous extract as 

phosphoric acid detected as the trimethyl ester (see Figure 20). Boiling these extracted 

oligomers 0.1 mol/L NaOH for 7 d reduced the phosphorus level to 0.036 % mass fraction. 

Again, the removed phosphorus species in the NaOH solution was identified as phosphoric acid. 

PBO oligomers, due to the limited solubility of TA in the reaction medium, are 

preferentially capped with DADHB during the manufacturing process (see Figure 1). However, 

in the model compound studies performed by So et al. [23, see compounds (3) and (5)] these 

researchers detected the presence of 4-(6-[4-(2-benzoxazolyl)phenyl]benzo(1,2-d;5,4-d’)-

bisoxazol-2-yl) benzoic acid and 4-(2-benzoxazolyl)-benzoic acid when their model compounds 

were dissolved in methanesulfonic acid. These species are known to exist in the PPA reaction 

medium as aryl-acetyl PPA esters (see Figure 1) and can remain after the neutralization 

procedure as aryl-acetyl phosphate esters. These types of esters are known to be stable under 

neutral conditions, while undergoing hydrolysis under basic conditions [24]. Therefore, it is 

probable that the additional phosphoric acid removed from our model systems by treatment with 

NaOH came from aryl-acetyl phosphate esters that are not typically found in processed PBO 

fibers. Some support for the supposition can be found in Figure 20 where the methyl ester of TA 

was detected as being extracted from the PBO model oligomers.

Analysis of the low-molecular mass PBO oligomers, synthesized as described in the 

experimental section, showed the presence of a peak at 688.5 u (see Figure 21). This compound 

was identified as being a mono-PBO phosphate ester (an aryl-phosphate) that differs structurally 

from the aryl-acetyl phosphate ester discussed above. The other compounds identified from 

peaks in Figure 21 are shown in Figure 22. Reanalysis of the solids by MALDI-TOF MS 

showed that the compound at 688.5 u was not removed by Soxhlet extraction. Interestingly, this 
21

compound was not removed by boiling the solid oligomers with 0.1 mol/L NaOH caustic 

solution. 

Noting the consistency of the model PBO oligomer results with those of the PBO fibers, 

the apparent stability of at least some of the non-extractable phosphorus to NaOH treatment is 

surprising since the working hypothesis considers the phosphorus to be chemically bound in the 

PBO oligomers as phosphate esters, and phosphate esters can be hydrolyzed under alkaline 

conditions [25]. To investigate this further, the model compound TPhP (see Figure 19) was 

refluxed in a 1 mol/L NaOH solution for 7 d. After the solution was concentrated and 

methylated, 95 % of the converted TPhP was found to be in the form of the dimethyl ester of 

monophenyl phosphate (DMPhP), with only 4.3 % being converted to TMP (see Table 2). 

To verify this surprisingly low conversion of TPhP to TMP, sodium phenyl phosphate 

dibasic dihydrate (DNaPhP) (see Figure 19) was refluxed in a 1 mol/L NaOH solution for 7 d. 

The conversion from DNaPhP to the trisodium phosphate salt (TNaP), as reflected in the 

methylated products of TMP and DMPhP by GC/MS, was less than 2 %. A similar experiment 

in a 1 mol/L NaOCH3 solution resulted in a slightly higher conversion of 6.9 % of DNaPhP to 

TMP (see Table 2). The results indicate that if the non-extractable phosphorus is chemically 

bound to the PBO polymer as the monoaryl phosphate ester (see Figure 19), it may be partially 

stable to the NaOH solutions that are commercially used to effect its removal.

From the above results, sodium phenyl phosphate dibasic dihydrate (DNaPhP) was 

converted to the acid, monophenyl phosphate, using an HCl solution with a final pH of 4. This 

solution was then placed in a sealed container and irradiated with UV light (sealed chamber 

approach). The conversion of monophenyl phosphate to phosphoric acid, as measured by the 

presence of TMP by GC/MS, was completed within 24 h (see Table 2). These results indicate 

that if the non-extractable phosphate is in the form of aryl-phosphate esters it may be removed by 

placing the fibers in an acidic medium and exposing it to UV radiation. The 1st set of PBO fibers 

that had been Soxhlet extracted twice and washed treated with 0.1 mol/L and 1 mol/L NaOH 

solutions for 7 d each was washed with pH 4 aqueous solution that was acidified with HCl. The 

washed fibers were divided into three portions. Each portion was placed in an aqueous medium 

acidified to pH 4 by HCl and irradiated with UV for 25 h. The acid medium was replenished as 

needed to keep the sample from becoming dry (open chamber approach). The acid mediums 

were combined, concentrated and tested for TMP, with very little being detected. 
22

Observing that the experiment on the DNaPhP model compound was performed in a 

closed system where the HCl could not escape, the 2nd set of PBO fibers that had been Soxhlet 

extracted and treated with 1 mol/L NaOH solutions for 7 d each was treated with pH4 aqueous 

solution as in the above procedure but this time the fibers and acidic solution were placed in a 

sealed system that has been described in the experimental section. GC/MS analysis of the 

aqueous solution indicated the presence of significant amounts of phosphoric acid in the form of 

trimethylphosphate (see Figure 23). It must be noted that the companion XRF analysis (see 

Table 1) also indicated a decrease in the phosphorus level of the acid treated and UV exposed 

fibers by the closed system. 

4 CONCLUSIONS

The data presented herein indicates that some free phosphoric acid is present in PBO 

fibers with a significant portion of the extractable phosphorus being n-octadecyl phosphate 

(either as the diacid or the diacid salt) that had been added as a processing aid. This result 

underscores the need to go beyond elemental analysis and determine the chemical identity of the 

residual phosphorus in the PBO fibers. The slight to moderate decrease in the residual 

phosphorus levels between the 1st set of PBO fibers and the 2nd and 3rd sets of PBO fibers 

suggests a possible change in the manufacturing process to better remove readily extractable 

phosphorus from the PBO fibers. With this potential reduction in residual phosphorus, the 2nd

and 3rd PBO fiber sets indicate that the primary remaining phosphorus is chemically bound to the 

PBO oligomers, possibly in the form of monoaryl phosphate esters that are resistant to effective 

removal by washing with NaOH. MALDI-TOF MS of low mass average molecular mass PBO 

oligomers synthesized in a manner consistent with the manufacturing process supports the 

presence of monoaryl phosphate esters in PBO fibers. Subsequent studies of triphenyl phosphate 

and monophenyl phosphate also support the stability of monoaryl phosphates to NaOH 

treatments. However, acid treatments of monophenyl phosphate showed complete conversion to 

phosphoric acid. Consistent with this latter result, acid treatment of PBO fibers that had been 

previously Soxhlet extracted and NaOH treated showed that additional phosphorus could be 

removed from the fibers in the form of phosphoric acid in a closed system that minimizes the 

loss of HCl. Interestingly, So et al. [7] deduced the presence of a monoaryl phosphate ester 
23

attached to PBO oligomers from their model compound studies using NMR. Consistent with the 

findings in this report, they observed that by placing one drop of water on the sample, the 

phosphate they deduced in the model compound studies as being in the form of a monoaryl 

phosphate slowly hydrolyzed under acid conditions. 
24

REFERENCES AND NOTES

1. H. Vogel; C. S. Marvel, J Polym Sci, 50, 511 (1961)

2. H. Vogel; C. S. Marvel, J Polym Sci A1, 34, 1125 (1996)

3. P. M. Cunniff; M. A. Auerbach; E. Vetter; D. J. Sikkema, "23rd. Army Science Conference",

Assistant Secretary of the Army (Acquisition, Logistics and Technology), Orlando, Florida, 

(Dec. 2002),

4. D.E. McLemore, Interim Summary of Finding on Toyobo's Zylon Fiber; Addressee: D. E. 

Wagner, Esq; July 20 2005.

5. P. J. Walsh; X. Hu; P. M. Cunniff; A. J. Lesser, J Appl Polym Sci, 102, 3517 (2006)

6. Y.-H. So; J. P. Heeschen, J Org Chem, 62, 3552 (1997)

7. Y.-H. So; J. P. Heeschen; B. Bell; P. Bonk; M. Briggs; R. DeCaire, Macromolecules, 31, 

5229 (1998)

8. G. A. Holmes; K. Rice; C. R. Snyder, J Mater Sci, 41, 4105 (2006)

9. X. Hu; A. J. Lesser Post-Treatment of Poly-p-Phenylenebenzobisoxazole (PBO) Fibers 

Using Supercritical Carbon Dioxide.; 2004.

10. J. Chin; E. Byrd; A. Forster; X. Gu; T. Nguyen; W. Rossiter; S. Scierka; L. Sung; P. 

Stutzman; J. Sieber; K. Rice, Chemical and Physical Characterization of Poly(p-Phenylene 

Benzobisoxazole) Fibers Used in Body Armor; NISTIR 7237; National Institute of Standards 

and Technology, Gaithersburg, MD 20899, Mar. 2005.

11. P. F. Jackson; K. J. Morgan; A. M. Turner, J Chem Soc Perk T 2, 11, 1582 (1972)

12. Sen, A., Tani, K., and Katoh, K., U.S. Patent 5393478

13. P. J. Walsh; X. Hu; P. M. Cunniff; A. J. Lesser, J Appl Polym Sci, 102, 3819 (2006)

14. J. F. Wolfe; F. E. Arnold, Macromolecules, 14, 909 (1981)

15. T. Kitagawa; H. Murase; K. Yabuki, J Polym Sci Pol Chem, 36, 39 (1998)

16. D. Z. Brunengraber; B. J. McCabe; J. Katanik; S. F. Previs, Anal Biochem, 306, 278 (2002)

17. A. Bhati, J Chem Soc, 729 (1963)

18. K. L. Busch, Spectroscopy, 16, 28 (2001)

19. Heller, S. R. and Milne, G. W. A., "EPA/NIH Mass Spectral Data Base", U.S. Government 

Printing Office: Washington, D.C., 1 (Molecular Weights 30-186) (1978) 1-987.
25

20. D. A. Bafus; E. J. Gallegos; R. W. Kiser, The Journal of Physical Chemistry, 70, 2614 

(1966)

21. F. W. McLafferty, Analytical Chemistry, 31, 82 (1959)

22. L. T. Sniegoski; E. White, Journal of Labelled Compounds and Radiopharmaceuticals, 20, 

303 (1983)

23. Y.-H. So; S. J. Martin; K. Owen; P. B. Smith; C. L. Karas, J Polym Sci A1, 37, 2637 (1999)

24. L. L. Cameron; S. C. Wang; R. Kluger, JACS, 126, 10721 (2004)

25. T. S. Whitesides; S. H. Hilal; L. A. Carreira, QSAR Comb Sci, 25, 123 (2006)
26

Table 1. Selected X-Ray Fluorescence Results for PBO Fibers, Model Oligomers and Liquids

(All values are mass fraction (%)).

Fiber Samples

ELEMENTS

Na Al Si P S Cl K Ca Fe

1st Set of Fibers

PBO Fibers as received 0.31 0.002 0.007 0.38 0.004 0.047 0.012 0.040

PBO Fibers after water wash 0.19 0.005 0.022 0.28 0.003 0.008 0.010 0.005 0.002

PBO damaged (by grinding) 0.20 0.013 0.009 0.30 0.004 0.007 0.010 0.009 0.029

PBO treated with 0.10 mol/L NaOH 8.6 0.033 1.7 0.25 0.002 0.009 0.006 0.006

PBO treated with 1.0 mol/L NaOH 0.45 0.065 0.49 0.25 0.008 0.029 0.017

Flakes from NaOH treated fibers 1.8 0.14 18 0.020 2.0 0.010 0.040

Fibers after removing flakes 0.58 0.038 0.71 0.28 0.008 0.012 0.010 0.024 0.005

Fibers after UV irradiation (open) 0.16 0.005 0.20 0.26 0.023 0.002 0.004

2nd Set of Fibers

PBO Fibers as received 0.20 0.004 0.32 0.001 0.014 0.040 0.005 0.033

PBO Fibers after water wash 0.12 0.009 0.012 0.29 0.002 0.011 0.013 0.035

PBO treated with 1.0 mol/L NaOH 0.45 0.035 0.34 0.27 0.003 0.014 0.009 0.007

Fiber after UV irradiation (closed) 0.052 0.025 0.69 0.21 0.064 0.002

3rd Set of Fibers

PBO Fibers as received 0.15 0.005 0.24 0.003 0.008 0.024 0.003 0.002

PBO Fibers after water wash 0.20 0.003 0.25 0.001 0.007 0.003 0.021

PBO Model Oligomers

Before extraction 0.008 0.016 1.4 0.027 0.010 0.013

After extraction 0.003 0.004 0.062 0.001 0.12 0.002 0.013

Treated 0.10 mol/L NaOH 0.61 0.020 0.12 0.036 0.001 0.10 0.19 0.034

Liquid Samples

Blank solvent 0.043 0.009 0.27 0.024 0.001 0.010

Extract from damaged fibers 0.034 0.021 0.50 0.026 Trace 0.006 0.002

Extract from PBO model oligomers 0.038 0.16 0.80 0.010

COMMENTS

Uncertainty: For P, the uncertainty (approx 95 % confidence level) is + 10 % to -50 %.

 For other elements, differences >100 % may be significant.

PBO polymer fibers were modeled as C14H10N2O2.

Liquid samples were modeled as H2O with P as PO4 and S as SO3.

Flakes were modeled as cellulose C6H10O5 because they contain weighing paper.

A blank cell means the element was not detected.

A note ‘trace’ indicates the element was detected, but was < 0.001 %
27

Table 2. Conversion of Triphenyl phosphate and Monophenyl phosphate to Phosphoric Acid in 

Caustic Solutions and Acid Solution plus UV Exposure

Samples Conditions Water solution Solid

TMP DMP MMP TPhP 

Triphenyl phosphate (TPhP) strong caustic treat (1N NaOH) 3.4% 74.5% 0.2% 21.9%*

4.3%+ 95.4%+ 0.3%+ 

Monophenyl phosphate, 

dibasic sodium, dihydrate (MPhP) 

TMP MPhP 

strong caustic treat (1N NaOH) 1.80% 98.20% 

strong caustic treat (1N NaOCH3) 6.90% 93.10% 

TMP MPhP 

UV-treat 0 h 0.2% 99.8% 

UV-treat 2 h 16.1% 83.9% 

UV-treat 12 h 73.4% 26.6% 

UV-treat 24 h 99.8% 0.2% 

*

Measured with ether extract from solid

+

Recalculated composition only in water extract.
28

Figure 1. Reaction scheme for the preparation of PBO polymer (adapted from So et al. [6,7]).

HO C C OH

O O PPA

YO C C OY

O O

+ 2 H2O

[A]

HO OH

+H3N NH3

+

O OH

+H3N NH3

+

YO OY

+H3N NH3

+

YO OY

H2N NH2

C

O

C

O

HO O

+H3N NH3

+

O OH

H2N NH3

+

C

O

C

O

HO O

+H3N NH2

[B]

N

OH

C

O

C

O

N

HO

OH H

NH3

+

H OH

NH3

+

H+ O OH

N NH3

+

HO O

+H3N N

[C]

[A]

O O

N N

XO O

H2N N

O OX

n N NH2

PBO Polymer

X=H or Y

P P

O

OH

Y= O OH

O

OH

Railford acyl migration

Terephthalic acid (TA)

4,6-diaminoresorcinol (DADHB)
29

Figure 2. Model compounds obtained from Wright Patterson Air Force Research Laboratories 

for studying hydrolytic and UV stability of PBO chain structure.
30

Figure 3. Relevance of model compounds shown in Figure 2 to the PBO repeat unit.
31

Figure 4. PBO structure model of AS fiber. (taken from reference 15 with permission)
32

Figure 5. 1000 W Solar Simulator used for exposing fibers to UV radiation.
33

Figure 6. Spectral outputs with selected attachments from 1000 W UV solar simulator shown in 

Figure 5.
34

Figure 7. Sealed chamber made of quartz used to exposed acidified PBO fibers to UV radiation 

using solar simulator shown in Figure 5. 
35

Figure 8. In-Situ Consumption Diazomethane Generator
36

Figure 9. Schematic Representation of carboxylic acid and phosphoric acid methylation by 

diazomethane.
37

Figure 10. Representation of ground PBO oligomer with small amount of THF/HCl 

(1 ml/1 drop) mixture and pressed with a spatula onto the MALDI target covered by parafilm.
38

Figure 11. MALDI-TOF-MS of 2,2’-(1,4-phenylene) bis(benzoxazolyl) (AF1).
39

Figure 12. MALDI-TOF-MS of 2,6-diphenylbenzo[1,2-d;5,4-d’]bisoxazole (AF2).
40

Figure 13. Total ion current trace of methylated phosphoric acid and peaks associated with the 

methylation procedure scaled in scaled in arbitrary units (a.u.) of intensity. These peaks are 

identified in Figure 14.
41

Figure 14. Compounds associated with methylation procedure (see Figure 13).
42

Figure 15. Trace DSQ II mass spectrometer used to identify phosphorus containing species 

extracted from PBO ballistic fibers. The mass spectrometer was eventually equipped with FPD 

and NPD detectors to aid in the detection and identification of phosphorus containing species. 
43

Figure 16. Total ion current (TIC) chromatograms (a) and (c) and parallel flame photometric 

detector (FPD) chromatograms (b,d) of methylated aqueous extract from PBO fibers tested under 

electron impact (EI) (a,b) and chemical ionization (CI) (c,d) test conditions. A.U. denotes 

arbitrary units of intensity. 
44

Figure 17. Electron impact (EI) and chemical ionization (CI) spectra of trimethyl phosphate 

(a,b) and long-chain alkyl phosphate (c,d). A.U. denotes arbitrary units of intensity.
45

Figure 18. Mass Spectrum of the trimethyl silyl derivative of 1-dodecyl-d25 phosphate (adapted 

from reference 22) showing a very small molecular ion at 420 u, indicative to the C12D25 alkyl 

group and the fragment ion at 245 u that reflects the subsequent loss of this group as a C12D23

radical from the molecular ion by the classic McLafferty + 1 rearrangement.
46

Figure 19. Chemical structure representation of phosphoric acid chemically bound to PBO 

oligomer as a monoaryl phosphate ester. To underscore the stability of the monoaryl phosphate 

ester bond, the chemical structure of triphenyl phosphate (a triaryl phosphate ester) and sodium 

phenyl phosphate dibasic dihydrate (a monoaryl phosphate ester), which are available 

commercially, is also shown.

 

 

 

O

N N

O O

N N

O

n

NH2

P

O

O

O

O

N

O

H

H

Phosphoric acid attached to PBO oligomer as monoaryl phosphate ester

P

O

O

O

O

Triphenyl phosphate

P

O

O

ONa+

ONa+

2 H2O

Sodium phenyl phosphate dihydrate dibasic
47

Figure 20. Total ion current trace showing the presence of trimethylphosphate and dimethyl 

terephthalate extracted from the model PBO oligomers. The unidentified peaks arise from the 

methylation procedure (see Figure 14).
48

Figure 21. MALDI-TOF MS of low molecular mass model PBO oligomers. A.U. denotes 

arbitrary units of intensity.
49

Figure 22. PBO oligomers identified in MALDI mass spectrum shown in Figure 21.

O

N N

O O

N N

n O

O

N N

O O

N N

n O

H2N

HO

O

N N

O O

N N

n O

H2N

HO

NH2

P

O

OH

OH

O

S1

S2

S3

O

N N

O O

N N

n O

H2N

O

N N

O O

N

n

S4

S5
50

Figure 23. (a) Total ion chromatography (TIC) and (b) FPD spectrum of UV-exposed 2nd

Caustic treated 1st PBO fiber Solution in EI mode of GC. (c) TIC and (d) FPD spectrum of UVexposed Water blank in EI mode of GC. A.U. denotes arbitrary units of intensity. 

P

O

H3CO OCH3 OCH3

TMP

2 4 6 8 10 12 14

0.0

2.0x107

4.0x107

6.0x107

Intensity (a.u.)

2 4 6 8 10 12 14

0.0

2.0x106

4.0x106

6.0x106

8.0x106

3.52

Intensity (a.u.)

Retention time (min)

3.54

2 3 4 5 6 7 8 9 10 11 12 13 14

0.0

2.0x107

4.0x107

6.0x107

Intensity (a.u.)

2 4 6 8 10 12 14

0.0

2.0x106

4.0x106

6.0x106

8.0x106

Intensity (a.u.)

Retention time (min)

(a) (c)

(b) (d)

2 4 6 8 10 12 14

0.0

2.0x107

4.0x107

6.0x107

Intensity (a.u.)

2 4 6 8 10 12 14

0.0

2.0x106

4.0x106

6.0x106

8.0x106

3.52

Intensity (a.u.)

Retention time (min)

3.54

2 3 4 5 6 7 8 9 10 11 12 13 14

0.0

2.0x107

4.0x107

6.0x107

Intensity (a.u.)

2 4 6 8 10 12 14

0.0

2.0x106

4.0x106

6.0x106

8.0x106

Intensity (a.u.)

Retention time (min)

(a) (c)

(b) (d)
51

APPENDIX A
52

Standard Operating Procedure for UV-Solar Simulator

Scope

This Solar Simulator is designed to simulate various solar conditions. This Solar Simulator 

produces an unfiltered xenon lamp spectrum. To approximate solar conditions for a variety of 

solar simulation applications we can modify the spectral output of the arc lamp by mounting 

various filters to match specific natural solar conditions.

Summary

Figure 1 shows light pass of a Solar Simulator. We can generate various conditions by changing 

air mass and/or bandpass filters. It generates uniform, collimated output beams in sizes from 4*4 

inches. Our Solar Simulator includes an electronic splitblade shutter. We can externally control 

this shutter from the Digital Control Panel on the illuminator housing, or via a hand held switch, 

contact closure, or logic level input. We can do automated exposure control with Digital 

Exposure Controller.

1000 W Solar Simulators.

 

Figure 1. Light of an Oriel Solar Simulator, showing location of air mass filter. 

Table1 and figure 2 show the summarized air mass filter type and their function and diagram of 

air mass filters. 

Air Mass 0 Filter (AM 0): this filter corrects the illuminator output to better match the solar 

spectrum in extraterrestrial space (ie outside the Earth’s atmosphere) per ASTM E490-73a. Used 

alone, this filter generates the Air Mass 0 spectrum. Additionally, it is the first filter element in 

all other Air Mass filter sets.
53

Air Mass 1 Direct Filter (AM 1 Direct): This filter set simulates the solar spectrum at ground 

level when the sun is directly overhead.

Air Mass 1.5 Direct Filter Set (AM 1.5 Direct): This filter set simulates the the direct solar 

spectrum with the sun at a zenith angle of 48.2o (ASTM E891).

Air Mass 2 Direct Filter Set (AM 2 Direct): This filter set simulates the direct solar spectrum 

with the sun at a zenith angle of 60.1o (ASTM E891).

Air Mass 1.5 Global Filter Set: This filter set corrects the solar simulator output to closely match 

the total (direct and diffuse) solar spectrum when the sun is at a zenith angle of 48.2o (ASTM 

E891).

Table 1. Air Mass Filters 

Figure 2. Diagram of solar air masses 

Table 2 shows the filters available and spectral output from 230 nm to 750 nm, when used with 

this simulator. 
54

Table 2. Bandpass Filters for Oriel Solar Simulators.
55

Safety Precautions for chemicals used in this procedure

Electromagnetic radiation with a wavelength between 10 nm and 400 nm is called ultraviolet 

radiation. Photobiologists use the term UVC for wavelengths to 280 nm, UVB for 280 nm to 

320 nm, and UVA for 320 nm to 400 nm, although there is disagreement on the 280 nm 

boundary. Radiation below 180 nm is referred to as vacuum UV

UV Radiation from Oriel® Lamp Sources

The deuterium and arc lamp sources, spectral calibration lamps, Solar Simulators and Flood 

Exposure Sources produce UV with wavelengths down to 180 nm and below, depending on the 

lamp and the envelope material of the lamp (the optics on the lamp housing may block the 

shorter UV wavelengths). Our Quartz Tungsten Halogen Sources emit some radiation down to 

220 nm. The UV intensity levels from some of these sources may be higher than those from the 

sun, and shorter wavelengths may be present. Carefully read this discussion as well as the Safety 

Instructions that are included with every UV source we ship, before operating the source.

Exposure Hazards

Exposure to UV radiation, even for short periods of time, can be hazardous. The damage depends 

upon the exposure time, the intensity of the radiation, the wavelength, and the individual's 

sensitivity to UV. Since we cannot sense (see) UV radiation, we are not protected by any 

aversion or blink response.

The Skin

UVB and UVC cause sunburn (erythema) and pigmentation (tanning). Long-term exposure 

results in loss of skin elasticity (premature aging). There is a well established connection 

between wavelengths below 320 nm and skin cancer (basal cell and squamous cell carcinoma) 

and growing concern over possible longer wavelength involvement. Action spectra for 

carcinogenesis peak at ~ 290 nm.

The Eye

Corneal absorption of UVB and UVC may cause conjunctivitis and a corneal inflammation 

called photo keratitis. Initial symptoms of photo keratitis are: slight discomfort, which, after 

prolonged exposure, can develop into a temporary yet severe discomfort, an inability to look at 

bright light, and the loss of clear vision. Conjunctivitis (welder's eye) produces an uncomfortable 

sensation, similar to sand in the eye. Our innocuous pencil style mercury calibration lamps can 

cause this problem.

Prolonged exposure to longer ultraviolet radiation, particularly UVA, may cause cataracts to 

form in the eye lens. Longer wave UVA may also penetrate to the retina and result in “blue 

blindness”.
56

Fig. 2 Threshold Limit Values for occupational exposure to ultraviolet radiation in an 8 hour 

period. These values for exposure of the eye or the skin apply to UV radiation from arcs, gas and 

vapor discharges, fluorescent and incandescent sources, and solar radiation, but they do not apply 

to UV lasers. (ACGIH ISBN: 0-9367-12-99-6)

UV Safety Precautions

The simplest thing to do if you don't need the ultraviolet is to get rid of it at the source. Use a 

lens or filter to accomplish this. If you require the UV then there are several precautions you 

should take to minimize exposure and reduce the hazards.

• Limit access to areas where UV sources are used 

• Post warning signs at the entrance to labs or other work areas using UV sources 

• Wear protective eyewear and gloves 

• Cover arms and neck and limit exposure time 

• Never look directly at the beam 

• Use a manual or electronic shutter to close the beam when the source is not in use 

• Use enclosed beam paths where possible

Ozone

If you note ozone odor smell persistently in an area remote from the fans, check the ozone levels 

and improve ventilation of the area.

Lamp Hazards

There is always a danger of lamp explosion due to mechanical failure

• Never touch the lamp with bare fingers or other contaminates

• Always wear appropriate gloves and impact-resistant goggles when handling the lamp

• Avoid any mechanical strain during handling

• Do not operate the lamp without all housing panels in place
57

Safety Guidelines

The U.S. National Institute for Occupational Safety and Health (NIOSH) recommends that 

exposure to UV energy be controlled and limited in the work place. Recommended maximum 

exposures are available, but these do not apply to photosensitive individuals or those exposed to 

photosensitizers.

The total intensity from 320 to 400 nm hitting an unprotected eye should not exceed 10 Wm-2 for 

periods longer than 1000 seconds. For shorter exposure times, the energy density should not 

exceed 104 Jm-2

Procedure

Quick Start UV Solar simulator

1. Turn on the lamp power supply 

(Do this process if you changed light source, usually this set up has done.  Set it to the 

maximum power level that you will allow your lamp to operate at, near the end of its life: 

normally 10% higher then desired operating point. (e.g. 1100 W for a nominally 1000W 

lamp – check for the safe power levels for the type of lamp you are using))

2. Start Lamp

3. Allow the system to stabilize for approximately 15 minutes.

4. Turn on Digital Exposure Controller while holding down the STOP/CLOSE button. (This 

action makes sure that you are starting at factor default set of values.)

5. Using TIMER/FLUX and SELECT buttons scroll until the μΑ LED is lit.

6. Check that light sensor is reading somewhere between 1 and 500 μA for best 

performance (use the START button to open the shutter, if present). ( Modify your 

light coupling method if the reading is outside of this range.)

7. Press the AUTO SETUP button and hold it until the AUTO-SETUP LED starts flashing 

(this may take up to 5 s). 

 ( The unit will bow open the shutter, if present, and investigate lamp’s output 

changes in response to power supply output changes. This data is used to optimize the 

intensity control function.  At the end of this step, the Digital Exposure Controller will 

save the min-max values of the possible control range and use its mid-point for a starting 

reference level. This will typically result, when FLUX CONTROL is later turned on, in 

power supply setting.  The shutter will now close and AUTO-SETUP LED will go off. 

Typically 10 to 20 seconds elapse from the beginning to the end of this function.  If 

FAULT LED lights up, see recovery section on the following page.

8. If closing of the shutter makes the μA readings go close to zero μA’s (light sensor 

mounted after the shutter), IDLE mode should be selected to keep power supply under 

control in this situation.

( Use the SET/ENTER and SELECT buttons to scroll through the LED’s until 

IDLE LED is lit.  Press SET/ENTER button for a moment until the IDLE LED flashes. 

 Use UP/DOWN buttons to choose 1 from the 0 and 1 options for the IDLE function. 

 Press SET/ENTER to save this selection.)

9. Press the FLUX CONTROL button to enable stable exposure.

10. Set exposure mode to automatic.
58

( Light up the MODE LED (TIMER/FLUX and SELECT buttons).  Enter the 

mode selection (SET/ENTER) and scroll to AUTO-TIME LED (UP/DOWN buttons). 

Save the selection (SET/ENTER).)

11. Light up the OPEN TIME LED (TIMER/FLUX and SELECT buttons) and enter the 

length of desired exposure (SET/ENTER, UP/DOWN, SELECT, SET ENTER buttons).

12. Press the START button to run your exposure.

Recovery from Fault Condition

1. Turn both the light source power supply and the Digital Exposure Controller off.

2. Disconnect the Power Supply Output control cable from the Digital Exposure Controller

3. Turn on the power supply and power up the lamp to the maximum setting

4. Turn on the Digital Exposure Controller.

5. Connect the Power Supply Output control cable back to the controller.

6. This resets the Power Supply operating point by releasing control from the Digital 

Exposure Controller, but it does nothing to resolve the cause of the fault. Please modify 

whatever condition caused the fault before running the auto setup again ( Check power 

supply limit settings  Check light sensor signal level  Check any other potentially 

“offending” candidates in your particular system)
59

APPENDIX B
60

Standard Operating Procedure for Derivatization with Diazomethane

Scope

This procedure is designed to alkylate residual acid impurities that may be found on poly(pphenylenebenzoxazole) [PBO] fibers and derivatize nanoscale defect sites along the polymer 

chain of PBO fibers and PBO model compounds. This methodology is needed so that these 

analytes can be analyzed by gas chromatography (GC) / mass spectrometry (MS), GC / Fourier 

transform infrared (FTIR) spectrometry, and matrix assisted laser desorption ionization 

(MALDI) – time of flight (TOF) MS. In addition, this procedure will be used to methylate any 

residual phosphoric acid (H3PO4) that may be extracted from PBO fibers by soxhlet extraction 

procedures.

Summary

Diazomethane is highly toxic, with early synthetic procedures stressing extreme care be 

exercised in the preparation and use of this material [1]. In this procedure, diazomethane is 

generated from the action of alkali on N–methyl-N–nitroso-p-toluenesulfonamide (diazald, see

Figure 1) that has been shown to be a safe precursor for generating diazomethane.

Figure 1. Reaction of potassium hydroxide on N-methyl-N-nitroso-p-toluenesulfonamide

Nitrogen gas passed through test tube #1 and into test tube #2 where the diazomethane is 

generated. The diazomethane and nitrogen gas mixture is then bubbled into a collecting vial (test 

tube #3) that contains methyl-t-butyl ether and the material to be derivatized (see Figure 2). 

Material need not be soluble in methyl-t-butyl ether

CH2N2

N-methyl-N-nitroso-p-toluenesulfonamide

S

N

O O

H3C

NO

CH3

KOH

potassium hydroxide Diazomethane

(Diazald (diazomethane precursor))
61

Figure 2. In-Situ Consumption Diazomethane Generator
62

The procedure described herein differs from the methods described in references 2 and 3 by the 

in-situ consumption of the millimole quantities of diazomethane that are generated from the N–

methyl-N–nitroso-p-toluenesulfonamide. This approach further minimizes the explosive hazards 

associated with this reaction. Diazomethane is commonly used to derivatize carboxylic acids (4) 

and chlorinated herbicides (2), phenols, and enols (5). Consistent with these results, 

diazomethane is also known to derivatize phosphoric acid to trimethylphosphate (6), a potential 

residual acid impurity in PBO fibers (see Figure 3). 

Figure 3. Schematic Representation of carboxylic acid and phosphoric acid methylation by 

diazomethane.

In addition, it is known that diazomethane reacts with amides, amines, hydroxyl groups on 

benzene rings, and other compounds containing labile hydrogen atoms. Interestingly, the 

commonly accepted hydrolytic and UV degradation pathways for PBO, suggests the possible 

formation of degradation products with labile hydrogen atoms (7). Since PBO does not contain 

labile hydrogen atoms, the diazomethane procedure may be useful in illuminating the presence of 

degradation sites along the chain of PBO fibers.

Safety Precautions for chemicals used in this procedure

Diazomethane is a toxic carcinogen that can explode under certain conditions. The

following general precautions must be followed when using this material:

1) Use only a well-ventilated hood - do not breathe vapors.

2) Use a safety screen.

3) Use mechanical pipetting aides 

4) Do not heat above 90 o

C - EXPLOSION may result.

5) Avoid grinding surfaces, ground glass joints, sleeve bearings, glass stirrers -

EXPLOSION may result. Therefore, all glassware used in this reaction must be 

fire-polished. No broken or chipped glass can be used with this reaction.

6) Store away from alkali metals - EXPLOSION may result.

O

P

O

O

O H

H

H

O

P

O

O

O CH3

CH3

CH3

CH2N2

R O

H

O

R O

CH3

O

CH2N2

Methylation of Carboxylic Acids

Methylation of Phosphoric Acid
63

7) Solutions of diazomethane decompose rapidly in the presence of solid materials 

such as copper powder, calcium chloride, and boiling chips. 

8) The diazomethane generation apparatus used in esterification procedure produces 

micromolar amounts of diazomethane to minimize safety hazards.

phosphoric acid 

C Corrosive

Risk Statements 34

34: Causes burns

Safety Statements 26-36/37/39-45

26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice

36/37/39: Wear suitable protective clothing, gloves and eye/face protection

45: In case of accident or if you feel unwell, seek medical advice immediately (show label where 

possible) 

diazald® (1)

E Explosive

Xi Irritant

Risk Statements 2-36/37/38-43

2 Risk of explosion by shock, friction, fire or other sources of ignition

36/37/38: Irritating to eyes, respiratory system and skin 

43: May cause sensitization by skin contact 

Safety Statements 15-26-35-36/37

15: Keep away from heat

26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice 

35: This material and its container must be disposed of in a safe way

36/37: Wear suitable protective clothing and gloves

potassium hydroxide

Hazard Codes C

C Corrosive

Risk Statements 22-35

22: Harmful if swallowed

35: This material and its container must be disposed of in a safe way

Safety Statements 26-36/37/39-45

26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice

36/37/39: Wear suitable protective clothing, gloves and eye/face protection 

45: In case of accident or if you feel unwell, seek medical advice immediately (show label where 

possible)

methyl-t-butyl ether

Hazard Codes F,Xi

F Highly Flammable

Xi Irritant
64

Risk Statements 11-38

11: Highly Flammable

38: Irritating to the skin

Safety Statements 9-16-24

9: Keep container in a well-ventilated place

16: Keep away from sources of ignition - No smoking

24: Avoid contact with the skin

trimethylphosphate

Hazard Codes T

T Toxic

Risk Statements 46-22-40

46: May cause heritable genetic damage

22: Harmful if swallowed

40: Possible risk of irreversible effects

Safety Statements 53-36/37-45

53: Avoid exposure - obtain special instruction before use

36/37: Wear suitable protective clothing and gloves

45: In case of accident or if you feel unwell, seek medical advice immediately (show label where 

possible)

carboxylic acid 

none

methanol

Hazard Codes F,T

F Highly Flammable

T Toxic

Risk Statements 11-23/24/25-39/23/24/25

11: Highly Flammable

23/24/25: Toxic by inhalation, in contact with skin and if swallowed

39/23/24/25: Toxic: danger of very serious irreversible effects through inhalation, in contact with 

skin and if swallowed

Safety Statements 7-16-36/37-45

7: Keep container tightly closed

16: Keep away from sources of ignition - No smoking

36/37: Wear suitable protective clothing and gloves

45: In case of accident or if you feel unwell, seek medical advice immediately (show label where 

possible)

Diethyl ether

Hazard Codes F+, Xn

F+: Extremely Flammable
65

Xn: Harmful

Risk Statements 12-19-22

12: Extremely Flammable

19: May form explosive peroxides

22: Harmful if swallowed

Safety Statements 9-16-29-33

9: Keep container in a well-ventilated place

16: Keep away from sources of ignition - No smoking

29: Do not empty into drains

33: Take precautionary measures against static discharges

Glassware

A. 2 fire-polished test tubes that have glass transfer lines for the nitrogen (N2) 

gas to pass to the adjacent test tube (see Figure 1).

B. 1 fire-polished test tube with no transfer line.

C. 1 fire-polished N2 purge inlet tube.

D. All test tubes must have openings for rubber stoppers.

E. 2 rubber stoppers that contain a single hole. 1 rubber stopper will be fitted 

with the N2 purge inlet tube. The second rubber stopper will be fitted on 

the transfer line of test tube #1 at a height that will allow it to fit into test 

tube #2. 

F. Plexiglass holder that holds the three test tubes and acts as an initial safety 

shield.

Reagents

A. Carbitol (Di(ethylene glycol) ethyl ether), Aldrich, 537616 100 g bottle (keep 

refrigerated). 90 day check for peroxides

B. Diazald (N-methyl-N-nitroso-p-toluenesulfonamide), Aldrich D2,800-0, 100 g bottle 

( keep refrigerated).

C. Potassium Hydroxide pellets, KOH, ACS grade. 

D. Ethyl Ether, Nanograde un-preserved, peroxide-free (stored under hood). Single use 

only. Test for peroxides prior to use.

E. 37% KOH: Weigh 37 grams of KOH into a 100 ml volumetric flask and bring to 

volume with nanograde water (store at 4 o

C).

F. Methanol, Chromatographic Grade

Procedure

A. Diazomethane Preparation: Refer to Figure 1.

1. Place diazomethane generator shown in Figure 1 into a clean hood that contains 

no heat or spark sources.

2. Use a N2 cylinder and install cylinder according to safety guidelines.
66

3. Add a sufficient amount of ethyl ether to test tube #1 so that when the purge 

inlet tube is in place the volume content of the ether is at least 50 % in the test 

tube volume but lower than the glass transfer arm that goes to test tube #2. 

4. Place the stopper with connecting tubing on tube #1 and adjust nitrogen purge 

so that liquid ethyl ether does not bubble out of the transfer arm into test tube 

#2.

5. Turn off N2 purge. 

6. Add 2-4 ml of carbitol to test tube #2. 

7. Add 4 ml of 37% KOH to test tube #2.

8. Place test tube #1 into test tube #2 via the rubber stopper making sure that the 

glass transfer arm from test tube #1 is well below the liquid level in test tube #2. 

The liquid level in test tube #2 with the glass transfer arm from test tube #1 

should be approximately 50 % of the volume of the test tube. If needed add 

more carbitol.

9. Turn on the N2 purge and make sure that the liquids in test tubes #1 and #2 

remain in their respective chambers.

10. Turn off N2 purge.

11. Place sample to be methylated into test tube #3 with (2 to 4) ml of methanol.

12. Connect test tubes 1, 2, and 3 together. Start N2 purge and make sure that the 

N2 bubbles into test tube #3 below the liquid line and at an acceptable rate. If 

needed add more methanol to tube #3.

13. With the N2 purge still on, gently break the rubber seal between test tube #1 and 

test tube #2. 

14. Add (0.2 to 0.4) g (solid) of the diazald to tube #2 and immediately 

reconnect test tube #1 and test tube #2. (Mixture will look like its boiling or 

bubbling when diazald is reacting.)

15. Turn holder around so that test tubes are facing away from the analyst.

16. Lower hood to less than 1⁄4 opening.

17. Reaction is complete when solution in test tube #3 remains yellow for two 

minutes.

18. Turn off N2 and break rubber seal.

19. To destroy the un-reacted diazomethane in test tube #2 by adding a small 

amount of water by pipette. The material in test tube #2 will turn from yellow to 

clear.

20. Place the contents of test tube #2 into a water soluble waste container.

21. Place a small amount of water in test tube #1. The ether on the top layer can 

then be evaporated since the ether was checked for peroxide prior to use and the 

evaporation process will be performed over water. 

REFERENCES AND NOTES

1. F. Arndt, in "Organic Synthesis: Collective Volume 2", A. H. Blatt, Ed., John Wiley & Sons, 

Inc.: New York (1943) p 165.

2. Diazomethane Generation SOP (PDF); 2003.

3. H. M. Fales; T. M. Jaouni; J. F. Babashak, Analytical Chemistry, 45, 2302 (1973)
67

4. J. March, "Advanced Organic Chemistry: Reactions, Mechanisms, and Structure", John 

Wiley & Sons: New York, (1992) p 383.

5. F. Ngan; M. Toofan, Journal of Chromatographic Science, 29, 8 (1991)

6. D. Z. Brunengraber; B. J. McCabe; J. Katanik; S. F. Previs, Analytical Biochemistry, 306, 

278 (2002)

7. G. A. Holmes; K. Rice; C. R. Snyder, Journal of Materials Science, 41, 4105 (2006)

Authors: Kathleen Flynn, Charles Guttman, and Gale A. Holmes